This is my take on the Sons of Horus colour scheme.

The main colours are green and silver, with red and gold accents

General Information:

My general method is to lay down all the base colours for the model, then do all the shading in the recesses before moving on to the highlights.

I don't own an airbrush so the recipe will mainly consist of Games Workshop spray cans and brush on paints.

Priming:

I find the metallic sprays from GW tend to be a little on the transparent side, so an initial undercoat of black helps.

1. Prime the model lightly with Chaos Black
2. Prime over that with Leadbelcher

Silver (Armour Trim)

I generally start with the armour trim so that any time I get paint on another piece its easy to cover later.

For grenades, replace Nuln Oil with Athonian Camoshade

1. Base with Leadbelcher
2. Shade the recesses with Nuln Oil
3. Highlight sharp edges and fine points with Stormhost Silver

Green (Armour Panels)

1. Base with Lupercal Green
2. Shade the recesses with Nuln Oil
3. Highlight the edges with Sybarite Green

Black (Armour Ribbing)

1. Base with Abaddon Black
2. Highlight the edges with Eshin Grey
3. Fine highlight along sharp edges with Dawnstone

Gold (Details)

1. Base with Retributor Armour
2. Shade the recesses with Agrax Earthshade
3. Highlight fine points and sharp edges with Stormhost Silver

Red (Lenses, Wraps, and Hair)

1. Base with Mephiston Red
2. Shade the recesses with Agrax Earthshade
3. Highlight the edges with Evil Sunz Scarlet
4. Finer highlight with Wild Rider Red
5. Highlight points with Fire Dragon Bright

Brown (Leather)

1. Base with Rhinox Hide
2. Shade the recesses with Agrax Earthshade
3. Roughly highlight the edges with Skrag Brown
4. Finer highlight with Ushabti Bone

Blue (Plasma)

1. Base with Sotek Green
2. Shade the recesses with Drakenhof Nightshade
3. Layer the middle with Temple Guard Blue
4. Highlight the edges with Baharroth Blue
5. Add points of Baharroth Blue mixed 1:1 with White Scar to the highest points